As a typical inverter circuit construction, an indirect ac power converter circuit that converts a commercial alternating current into a direct current via a rectifying circuit and a smoothing circuit and outputs a desired alternating current by a voltage type converter is generally used. On the other hand, as a system to directly obtain an ac output from an ac voltage, a direct power converter apparatus represented by a matrix converter is known, and this obviates the need for a large-size capacitor or reactor for smoothing the voltage pulsation due to the commercial frequency. Therefore, downsizing of the converter can be expected, and the converter has attracted attention in recent years as a next-generation power converter apparatus.
As a conventional direct power converter apparatus, there has been a direct power converter apparatus having a PWM rectifier that converts a three-phase ac voltage into a dc voltage and a PWM inverter that converts the dc voltage converted by the PWM rectifier into a prescribed three-phase ac output voltage (refer to, for example, JP 2004-266972 A).
The direct power converter apparatus generates a trapezoidal waveform instruction signal on the basis of an input current instruction and compares the trapezoidal waveform instruction signal with a carrier signal to generate a PWM modulation signal for turning on and off the switching circuit of the PWM rectifier. Moreover, the direct power converter apparatus compares a triangular wave obtained by transforming the carrier signal with an output voltage instruction to generate a PWM modulation signal for turning on and off the switching circuit of the PWM inverter.
However, because the direct power converter apparatus generates the trapezoidal waveform instruction signal by calculation on the basis of an input current instruction, the direct power converter apparatus has a problem that the operational load of the control section increases.
Moreover, because the direct power converter apparatus needs to transform the carrier waveform on the PWM inverter side, the direct power converter apparatus has a problem that the modulation waveform generation is complicated, and the control circuit becomes complicated. There is a further problem that the circuit of the control section becomes complicated also when a carrier generator circuit to supply a carrier signal is separately used for the PWM rectifier and the PWM inverter.